1. Technical Field
The present disclosure relates in general to network communication and, in particular, to an improved congestion management system for packet switched networks.
2. Description of the Related Art
As is known in the art, network communication is commonly premised on the well known seven layer Open Systems Interconnection (OSI) model, which defines the functions of various protocol layers while not specifying the layer protocols themselves. The seven layers, sometimes referred to herein as Layer 7 through Layer 1, are the application, presentation, session, transport, network, data link, and physical layers, respectively.
At a source station, data communication begins when data is received from a source process at the top (application) layer of the stack of functions. The data is sequentially formatted at each successively lower layer of the stack until a data frame of bits is obtained at the data link layer. Finally, at the physical layer, the data is transmitted in the form of electromagnetic signals toward a destination station via a network link. When received at the destination station, the transmitted data is passed up a corresponding stack of functions in the reverse order in which the data was processed at the source station, thus supplying the information to a receiving process at the destination station.
The principle of layered protocols, such as those supported by the OSI model, is that, while data traverses the model layers vertically, the layers at the source and destination stations interact in a peer-to-peer (i.e., Layer N to Layer N) manner, and the functions of each individual layer are performed without affecting the interface between the function of the individual layer and the protocol layers immediately above and below it. To achieve this effect, each layer of the protocol stack in the source station typically adds information (in the form of an encapsulated header) to the data generated by the sending process as the data descends the stack. At the destination station, these encapsulated headers are stripped off one-by-one as the data propagates up the layers of the stack until the decapsulated data is delivered to the receiving process.
The physical network coupling the source and destination stations may include any number of network nodes interconnected by one or more wired or wireless network links. The network nodes commonly include hosts (e.g., server computers, client computers, mobile devices, etc.) that produce and consume network traffic, switches, and routers. Conventional network switches interconnect different network segments and process and forward data at the data link layer (Layer 2) of the OSI model. Switches typically provide at least basic bridge functions, including filtering data traffic by Layer 2 Media Access Control (MAC) address, learning the source MAC addresses of frames, and forwarding frames based upon destination MAC addresses. Routers, which interconnect different networks at the network (Layer 3) of the OSI model, typically implement network services such as route processing, path determination and path switching.
A large network typically includes a large number of switches, which operate somewhat independently. Switches within the flow path of network data traffic include an ingress switch that receives incoming data packets and an egress switch that sends outgoing data packets, and frequently further include one or more intermediate switches coupled between the ingress and egress switches. In such a network, a switch is said to be congested when the rate at which data traffic ingresses at the switch exceeds the rate at which data traffic egresses at the switch.
In conventional networks, when a switch in a data flow path is congested with data traffic, the congested switch may apply “back pressure” by transmitting one or more congestion management messages, such as a priority-based flow control (PFC) or congestion notification (CN) message, requesting other switches in the network that are transmitting data traffic to the congested switch to reduce or to halt data traffic to the congested switch. Conventional congestion management message may specify a backoff time period during which data traffic is reduced or halted, where the backoff time may be determined upon the extent of congestion experienced by the congested switch.
Conventional congestion management messages may not provide satisfactory management of network traffic, however. Conventional congestion management schemes are voluntary in that the switches sourcing the congesting data traffic are free to ignore the congestion management messages of the congested switch and to continue to transmit excess data traffic, which ultimately will be dropped by the congested switch. Further, a delay occurs between when congestion is detected by the congested switch and when the other switches of the network stop sending data traffic to the congested switch. During the delay, excess data traffic can be dropped by the congested switch. Thus, the conventional techniques of congestion management are reactionary and can require the communication protocols utilized to transport the data traffic to recover dropped data traffic. Conventional congestion management is particularly inadequate in scenarios in which the flow path of data traffic includes a large number of series-connected switches. In such cases, congestion may start at the egress switch and then continue build toward the ingress switch in domino fashion, with data traffic being dropped all along the line. The processing and latency required to recovery traffic dropped in response to congestion is further exacerbated when the data traffic is communicated with lossy lower layer protocols.